1. Field of the Invention
The present invention relates to laundry machine drums and in particular to the form of perforations in the laundry machine drum skin and to methods of forming same.
2. Summary of the Prior Art
In laundry machines, of both horizontal and vertical axis varieties, it is well known to provide a drum having a metal, for example stainless steel, drum skin. In general this drum skin is provided with an arrangement of a plurality of openings therethrough. These openings are for example plain holes through the drum skin which may be formed by punching or by lancing from the inside surface of the skin.
In a washing or rinsing operation wash liquids may pass through the drum skin in one or other direction. In a dehydration operation wash liquids are extracted from a saturated clothes load retained within the drum by centrifugal force when the drum is spun at high speeds.
It is known in the prior art that burrs on the outermost edge of the sheet metal at the holes are dangerous to the fingertips of a user of a laundry machine and/or to laundry. The burrs may catch laundry fibres which may pass outwardly through the holes and become caught.
Furthermore it has been found that there is a limitation on maximum drum spinning speeds that can be safely used where a plain hole perforation is adopted. Where the spinning speed reaches above a certain level and the centrifugal forces become too great, either the laundry fabrics are drawn outwardly through the plain holes or the fabric spanning the plain hole tears outwardly at its centre under the forces exerted. If the laundry extrudes outwardly through He holes it may be tom when removing the laundry from the surface of the drum even though burrs may not be present at the outer edges of the plain holes.
It is accordingly an object of the invention to provide a laundry drum for a washing machine incorporating perforations which will at least go some way towards overcoming the above disadvantages and/or to provide a method of forming such perforations.
In a first aspect the invention consists in a laundry machine drum having a sheet material skin including an arrangement of a plurality of perforations therethrough, each of one or more of said perforations including:
a shear cut in said sheet material, the sheet being deformed in the region of said shear cut such that the edge of the sheet material of one side of said shear cut is offset from the edge of the sheet material of the other side of said shear cut over at least some of the length of said shear cut such that an opening is formed between said offset edges and the apparent area of said opening is greater when viewed from at least one direction substantially parallel to the general plane of said drum skin in the region of said perforation than when viewed from a direction substantially perpendicular to tie general plane of said drum skin in said region of said perforation.
In a further aspect the invention consists in a method of forming a perforation in a laundry machine comprising operating on a sheet material with a punch and corresponding die,
said punch having a leading face, and a shearing edge defining one edge of said leading face,
said die having a leading face and a complementary shearing edge to said punch shearing edge,
said leading faces and shearing edges of said punch and said die formed such that movement of said punch in an advance direction relative to said die causes said shearing edge of said punch to overlap with said shearing edge of said die at at least the middle of said shearing edges, and to overlap progressively less away from the middle of said shearing edges, to produce a sheared cut in a material placed there between which progressively reduces in displacement from its middle to its ends.
In still further aspect the invention may broadly be said to consist in a laundry machine drum having a sheet material skin including an arrangement of a plurality of perforations therethrough, each of one or more of said perforations being formed in accordance with a method as set forth above.
In a still farther aspect the invention may broadly be said to consist in a laundry machine drum having a sheet material skin including an arrangement of a plurality of openings therethrough, at least one said opening having a form such that the apparent area of said opening is greater when viewed from at least one direction substantially parallel to the general plane of said drum skin in the region of said perforation than when viewed from a direction substantially perpendicular to the general plane of said drum skin in said region of said perforation.
To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims, The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.